Okay, I have just ordered a new 20 fm transmitter, and i have an 1/2 dipole from FRB from an old project. I have no where to mount the antenna other then the tree in my back yard, the problem is, its about 60 feet from ground, and 50 feet from house. How much power do you suppose i would lose by using that much coax? and How much would the coax cost?
You should invest in an SWR meter. It should have a field strength meter. The problem is that one at FM frequencies is hard to find. But check eBay. Make sure that you have some way to mount the antenna so that NONE of it touches the tree. It might not ground it out completely, but it will impair the output and directionality. Which one of Stephens dipoles do you have?
IMHO, I wouldn't use anything less than RG-213 (an update of RG-8). Even then, be prepared to lose a good portion of your power in the coax.
Does "20 FM" mean a 20 watt transmitter?
If you have an antenna 60 ft. in the air, with 20 watts out of the transmitter, even with the line loss, you'll still have a useable signal in the area.
Yes, i have a 20 watt fm transmitter, sorry for not making that clear. I would need around 100-120 feet of coax, on the website you showed me cmradio, the only types of rg-8x coax are the 3060 and marine. This website seems to have fairly good prices, and i would love to buy from them. I have the 40 dollar dipole kit on FRB's store. I'm thinking about also purchasing a jpole from another website, as i dont have the tools or the time to make one. Thanks for the help, Andrew.
Looking at the loss chart for loss/100' at 100MHz, The RG8X (3060 or marine) has 3.8 dB, while the full size RG8 and 213 Radioguy suggested has 1/2 that.
It'll break down to budget and skill. 8X takes less skill with a soldering iron, but 8 and 213 is better stuff for that run.
The cool thing about 8X though, is it's easier to find a BNC connector to fit it (Digikey, Mouser, etc.) while 8 and 213 are best with an N-connector.
Fuggedabbout those crappy PL259/SO-239 at FM freq's .... you'll lose as much in a set of them as in your coax run (unless you go teflon).
Post by RadioFreeEuropea on Jan 25, 2011 8:47:48 GMT -6
I tested diffrend coaxcables, i drive 1W in 100m roll diffrend cables. Powers measurent other end of cable Results: RG58 0.3W RG213 0.8W RG8B 0.5W RG8U 0.5W RG174 0.2W RF 400 0.7W
I use RG213 whit all transmmitters Longest cable is 75M, it is for SW dipol.
RFEI SW MW LW FM Freeradio broadcasting isn't crime, it's my way life!
Here's what it says on my cable: " Prime P6200BX RG6 18awg CCS 60%A1 Braid swept to 3ghz" So obviously I'm using RG6. It's about about 50' from the transmitter to the antenna, which is a 1/4 ground plane mounted on a chimney. It's about 50' off of the ground. I don't have a field strength meter, but I do know that on a good day the signal from my 15 watt reaches 5 to 8 miles.
Fuggedabbout those crappy PL259/SO-239 at FM freq's .... you'll lose as much in a set of them as in your coax run (unless you go teflon)
I have never had an issue with them but then I have always ran under 10 watts of power on FM. I wonder what the average loss for using that type of connector is? I ask because I have not noticed a difference between them and other UHF types as long as the PL259 connectors were soldered and braided with care. They should be good up to 300MHz so for FM broadcast band they technically should be fine. I think most peoples problem is not properly soldering on the connectors and stripping the coax with the correct tool. Here's a good link showing how to do it the right way.. www.eham.net/articles/5071
Post by Ozone Express Radio on Jan 25, 2011 14:15:40 GMT -6
What about LMR400? I've been using that almost exclusively and it is very good stuff. Very low-loss, but also quite pricey.
I've noticed a drop in my SWR reading simply by switching from RG58 (good quality) to the LMR400 and doing nothing else. It also doesn't mind those long runs either.
"I ask because I have not noticed a difference between them and other UHF types as long as the PL259 connectors were soldered and braided with care".
Again, IMHO, I've had good success with the PL259 connectors but I make sure to use teflon or those with "clear" insulators. I would avoid those that are solid "colored".
I wonder what the average loss for using that type of connector is? I ask because I have not noticed a difference between them and other UHF types as long as the PL259 connectors were soldered and braided with care.
If your SWR is low, at 144MHz, we measured about 2dB for the average "10-4 good buddy" type. 0.9dB for cadmium plated w/teflon.
They are non-constant impedance (they are the only RF connector still in use with a non-constant impedance. Even a TV F-connector has a constant impedance), so their loss goes up with SWR. On 2M, they are 6-8dB loss (and they get hot because of this), depending on the insulation, with a 2:1 SWR.
I use LM400, which cost around .93 cents a foot and only high quality PL259 connectors. It's true that low end PL259 connectors can be a real pain to use and cause trouble.
I have a guy who is mounting a dipole to the side of a telephone; he will be using clamps like those used to mount conduit to walls (look a little like an ohm symbol). The elements will be about 25" from the pole.
My cable run is 30ft and I can get 2 miles in the city @ 15ft above ground and 100milliwatt input; about four miles short of my old desert coverage.
I'm amazed that you get that far at 100 mil. I have the Ramsey FM25B, which I like a lot. I have an upgraded version of their TM-100 dipole. I was able to get better copper-clad ladder wire and made my own balun. My feed line is 4' and I'm on the top floor of a 4 story building, about 50'. I'm good for four square blocks. Of course it's a backup for my 15 watt, which gets out 8 to 10 miles on a good day.